There are mainly two categories of obstetric suction devices, those made from an elastically yielding material, such as rubber, and those made from a rigid material, such as metal, e.g. stainless steel. There is a difference of opinion about the advantages of one category or the other, but extensive clinical use has shown that injuries are more frequent when using a soft suction cup than when using a hard one. The injuries which may occur in connection with the use of these suction devices are mainly contusions and are of a considerably less serious type than those usually occuring when deliveries are performed with the aid of obstetric forceps.
During the delivery process the head and body of the fetus are adjusted in the various sections of the delivery canal in such a manner, that the fetus may pass with the least possible resistance. To obtain this adjustment in the case of a fully dilated cervix it may be necessary, in the second phase of the delivery, to apply the suction cup over the rear fontanelle of the fetus, so that the center of the cup is directed towards sutura sagitalis. Previously known suction cups of the kind mentioned above are provided with a pulling handle attached to the central portion of the cup. Due to the central location of the handle on top of the suction cup, the tractive force will even be distributed when the handle is pulled at right angles to the suction surface, whereas a pulling force applied at an angle to the suction surface either will cause the suction cup to be pulled loose or cause a portion of the edge of the suction opening to apply a pressure against the head of the child. This pressure may be large enough to cause severe pressure marks.
Since the application of the suction cup has to be made within the uterus, it is important that the suction cup does not occupy a large space. Above all it is important that the cup does not have any projecting portions which may cause damages or inconvenience.